This invention relates generally to centrifuges and generally to apparatus and methods for placing tubes in centrifuge rotors. Still more particularly, this invention relates to apparatus and methods for holding a small tube in a bucket in a centrifuge rotor that was originally designed to accommodate tubes having larger diameters.
In chemical laboratory procedures it is often desirable to use small diameter tubes to hold a sample for exposure to the effects of a centrifugal force field. Centrifuges rotors are commonly made to hold a tube having a larger diameter than the small tubes that are sometimes used to hold the sample. It is common practice to insert the small tube in an adapter formed of a polymeric substance. Such adapters are ordinarily formed as a unitary piece of the polymeric substance shaped as hollow tubes having an outer diameter dimensioned to fit suitably within the centrifuge bucket and having an inner diameter dimensioned to receive the small tube. The function of the adapter is to fill the space in the bucket around the smaller tube.
U.S. Pat. No. 3,050,239 to Williams discloses an adapter for carrying microtubes while they are centrifuged in a peripherally slotted rotor. The adapter disclosed by Williams is a substantially planar member having an array of apertures therein. a microtube may be inserted into each aperture. The adapters are slidably receivable within slots arcuately spaced about the periphery of the rotor.
Microtubes may also be centrifuged while carried by the buckets of a swinging bucket-type centrifuge rotor. In such rotors each bucket is pivotally mounted between trunion pins carried on angularly spaced adjacent arms that emanate for the rotor hub. A typical adapter for swinging bucket rotors is sold by E. I. Du Pont Nemours and Company, Inc. under the trademark "Sorval". various other adapters are disclosed in U.S. Pat. No. 4,451,250 to Romanauskas, U.S. Pat. No. 3,998,383 to Romanauskas et al., U.S. Pat. No. 3,027,799 to Weichselbaum, and U.S. Pat. No. 4,484,907 to Sheeran, Jr.
Since the adapter is usually made of a different material than the tube, the behavior of the adapter under centrifugal load differs from that of the tube. In most cases the tube plastically deforms as it expands to fill the interior of the adapter. When the centrifugal load is removed from the tube, the tube must be extracted from the adapter for subsequent chemical processes to be performed on the sample.
However, because of the plastic deformation of the tube within the adapter, it is often extremity difficult to remove the tube from the adapter. It is common practice for laboratory personnel to manually extract centrifuge tubes from adapters by grasping the upper end of the tubes with a hemostat or other similar device. Prior adapters require that the length of the centrifuge tube exceed the length of the portion of the adapter that closely fits upon the body of the tube. Therefore, the adapters and centrifuge tubes must be selected so that it is possible to grasp the open end of the tube to remove the tube from the adapter. Difficulties in removing the small tube from the adapter are time consuming and often have deleterious effects on the density gradient of the layers in the centrifuged sample.